The length of the B and global C timer can be adjusted on the Class B/C Timer Setup Page (Pg. 634). This page can be found under "Timers Setup" -> "Class B/C Timer Lengths". Both B timers will count down from any RESET button press, and when they reach zero will arm the inputs of that class. Generally the B2 timer should be the shorter timer, intended for items that should clear during the very initial startup of the engine.
The maximum C time can be optionally entered on this page, or set to 0 if not used. If used, this timer will count down from the RESET button press, and when it expires will globally arm all C inputs, even if they have not cleared yet. This prevents a C contact from never arming before the operator leaves the site.